Some vehicle engine systems utilize both direct in-cylinder fuel injection and port fuel injection. The fuel delivery system may include multiple fuel pumps for providing fuel pressure to the fuel injectors. As one example, a fuel delivery system may include a lower pressure fuel pump (or lift pump) and a higher pressure (or direct injection) fuel pump arranged between the fuel tank and fuel injectors. The high pressure fuel pump may be coupled to the direct injection system upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. The high pressure pump may also be powered by a driving cam that is coupled to a crankshaft of the engine. A solenoid activated inlet check valve, or spill valve, may be coupled upstream of the high pressure pump to regulate fuel flow into the pump compression chamber. The spill valve may be energized synchronously to the position of the driving cam or engine angular position. As such, a controller or other type of computerized device is used to control the timing of the spill valve in relation to pump piston movement. However, the spill valve may become out-of-sync with the driving cam, causing a mistiming between spill valve actuation and movement of the pump piston. This event is known as spill valve timing error.
In one approach to monitor spill valve timing, shown by Takahashi in U.S. Pat. No. 6,953,025, the spill valve is controlled by using a cam angle signal, wherein a relation exists among a crank angle signal, cam angle signal, control signal supplied to the spill valve, and stroke of the pump cam. The inventors herein have recognized that a method is needed where the spill valve error can be corrected on-board the vehicle without depending on angular position sensors. The fuel supply control apparatus of U.S. Pat. No. 6,953,025 utilizes position sensors to modify spill valve timing. The inventors herein have proposed methods for correcting spill valve timing error by monitoring fuel rail pressure and apparent closing timing of the spill valve.
Thus in one example, the above issues may be addressed by a method, comprising: adjusting duty cycle of a high pressure pump to correct a timing error of a spill valve based on a zero flow function for the high pressure pump, the spill valve regulating fuel flow into a compression chamber of the high pressure pump and the zero flow function based on a change in pump duty cycle relative to a resulting change in fuel rail pressure. In this way, spill valve timing correction may be learned on-board the vehicle while utilizing fuel rail pressure readings to control the spill valve. Also, the spill valve timing correction methods explained herein may monitor and analyze data produced by the fuel system in different operating modes without invasively disrupting the fuel system. The operating modes may include various idling and/or fueling conditions such as fueling the engine via port fuel injection only or direct injection only. Furthermore, since the correction methods may not require additional physical components than are already incorporated in the fuel system, costs associated with the fuel system may be reduced as compared to other correction methods that may require expensive additional components. As such, this may allow the complexity of the control system of the vehicle to be reduced, thereby reducing power consumption and cost of the control system.
Using the flow function to adjust pump duty cycle may involve determining an offset of the flow function. The offset may be used to either delay or accelerate the closing of the spill valve so as to synchronize the spill valve timing and compression stroke of the pump piston. Finding the offset can be accomplished in several ways. For example, while not direct injecting fuel into an engine, a series of pump duty cycles are commanded while determining the responsive fuel rail pressures to form a series of operating points. Those operating points can then be plotted to form a zero flow function to find an offset value that represents the mistiming between spill valve actuation and pump piston movement.
In a related example, while direct injecting fuel into an engine, a multitude of pump duty cycles are commanded at selected fuel rail pressures along with fractional volume of liquid fuel pumped, forming a series of lines that can be used to find intercepts that correspond to zero flow rate data. The zero flow rate data, a series of operating points at zero flow relating fuel rail pressure and duty cycle, can then be plotted to form a zero flow function to find an offset value that may be used to correct spill valve timing error.
It is noted that pump duty cycle refers to controlling the closing of the pump solenoid activated inlet check valve (spill valve), where the spill valve controls the amount of fuel pumped into a fuel rail. For example, if the spill valve closes coincident with the beginning of the engine compression stroke, the event is referred to as a 100% duty cycle. If the spill valve closes 95% into the compression stroke, the event is referred to as a 5% duty cycle. When a 5% duty cycle is commanded, in effect 95% of the displaced fuel volume is spilled and the remaining 5% is compressed during the compression stroke of the pump piston. Duty cycle is equivalent to spill valve timing, in particular the closing of the spill valve.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.